1. Field of the Invention
The present invention relates to an aerodynamic lift apparatus and a high pressure jet engine therefor, more particularly it relates to such an apparatus and said engine which is declared in my co-pending invention entitled "hybrid internal combustion engine", both having the major application in vertical-takeoff-and-landing (VTOL) aircraft.
2. Description of the Prior Art
Air transportation, with its three dimensional movement, is inherently superior than surface transportation. To get to the third, the vertical, dimension, gravitational pull needs to be overcome, in other words, a lift force is needed. The direct way to do this is by propulsion, such as using the gas exhaust thrust of a jet or rocket engine. The indirect way is by air floatation, such as airships, utilizing the fact that everything on and above the surface of earth is immersed in an air mass, the atmosphere. Winged (fixed or rotary) aircraft use a third way, i.e. by the lift force produced from the difference of pressures against the upper and lower surfaces of an airfoil (wing or rotary blade) during its rapid motion in the air pursuant to the Bernoulli principle.
All three ways have advantages and disadvantages. The first one, the propulsion method, is straightforward to achieve but needs large engine power to produce the required thrust. The second one, the floatation method, is cheap in energy cost but needs either a large body to carry enough volume of a light weight gas as in airships or a large airfoil to contain large volume of air as in motorized gliders, hence limiting its performance. The third one, the airfoil lift method, is the practical one due to its better lift-to-weight ratio, but it needs a high speed of the airfoil relative to the ambient air to effect enough pressure difference. Because of the need for this high speed, aircraft using the airfoil lift method, as almost all the contemporary fixed-wing aircraft do, suffer greatly from many disadvantages stemming from this requirement, especially during takeoff and landing, such as those in terms of safety, noise and structural weakness in the wings, as well as other associated disadvantages such as need of long runway and hence airport, fuselage shape constraint, etc.
Various methods have been devised in one way or another to mix or to combine some forms of these three methods in an attempt to achieve the optimal solution for the vertical movement, especially during takeoff and landing, they thus fall under the category of VTOL aircraft. A large group of the VTOL solutions focus on modifying, improving, or augmenting the rotary wing aircraft, commonly known as helicopters. This is not surprising since they are the main VTOL aircraft in commercial application, but they have the major disadvantages of low performance in terms of speed, payload, stability, safety, maneuverability, altitude and drag, and other related disadvantages such as noise, mechanical complication, high costs of manufacturing and maintenance, etc., almost all due to the propeller (commonly called rotor in helicopter application) lift system it uses, including the need for a tail rotor to counter the torque generated by the main rotor.
The three methods, either alone or in combination, with current state of the art, have not solved the VTOL problem in a commercially viable manner. Therefore, other forces are being explored, one is the airfoil lift force produced in a reverse manner. It is mentioned heretofore that this force is generated on the airfoil through its motion relative to the air pursuant to the Bernoulli principle. Since this motion is a relative one, either that the airfoil moves against the air, or vice versa, can produce the lift. Accordingly, a large group of VTOL (or STOL, S stands for `short`, meaning short takeoff distance) solutions focus on generating or blowing air streams around the airfoil to produce (or enhance) the pressure difference, hence the lift. U.S. Pat. No. 5,203,521 to Day (1993), U.S. Pat. No. 5,170,963 to Beck (1992), U.S Pat. No. 5,046,685 to Bose (1991) U.S. Pat. No. 3,785,592 to Kerruish (1974) and U.S. Pat. No. 2,801,058 to Lent (1957) all show a VTOL aircraft with the method of blowing air streams around airfoils.
If the airfoil method is to be used satisfactorily in the above-mentioned manner, enough quantity and velocity of the air stream need to be generated to blow around the airfoil in a way such that substantial pressure difference is created therewith. Although the motion involving the airfoil and the ambient air is a relative one, but for the case of an airfoil moving against the air, as winged aircraft does, the Bernoulli theorem is applied by simply drawing an imaginary closed body fully enclosing the airfoil. On the other hand, for the case of air moving against an airfoil, if the Bernoulli theorem is to be likewise applied, the quantity of the air needs to be such that the airfoil is entirely immersed in the moving air stream. This means that the power source needs to have the capacity to supply this quantity of air mass--called working substance (WS) to differentiate it from air used as fuel--the rate of which is proportional to the velocity of the air stream and to the cross-sectional area of the airfoil. Since the magnitude of the lift generated by the airfoil is generally proportional to the square of this velocity, the larger the lift is required, the higher the velocity must be, and the more WS is needed. The US patents cited above do not teach how to generate such enough amount of WS and hence do not show whether the magnitude of the lift is commercially significant.
Clearly, blowing air around an airfoil doesn't seem a practical method to generate commercially significant lift force: it needs not only a powerful engine, the same problem for the propulsion method, but also a large amount of air (the WS) for this purpose, this air supply problem being even not addressed in prior arts. However, a closer examination of the two pressures at the upper and lower surfaces of an aircraft wing reveals a useful fact: the pressure under the airfoil roughly equals the ambient air pressure and it is the lower-than-atmospheric pressure at the upper surface which contributes mostly the pressure difference. Accordingly, if there can exist a lower-than-atmospheric pressure above the surface of a body which needs not to be in the shape of an airfoil, then a lift force will be produced on the body by the balance of pressure against the body--call it pressure force for reference, hence the method of using it the pressure force method, since airfoil is not relevant now.
U.S. Pat. No. 5,054,713 to Langley et al. (1991), U.S. Pat. No. 5,031,859 to Cunningham (1991), U.S. Pat. No. 4,674,708 to del Castillo (1987), U.S. Pat. No. 4,566,699 to Cucuzza (1986), U.S. Pat. No. 3,697,020 to Thompson (1972) and U.S. Pat. No. 2,726,829 to Hillis (1955) seek to use this method, but the geometries of their upper surfaces do not clearly show the existence of the lower pressure and how it is maintained, and they do not address and hence solve the WS supply problem. Except U.S. Pat. No. 3,697,020, the other five patents do not specifically refer to the pressure force phenomena despite the fact that they make the use of blowing gas streams over an upper surface. U.S. Pat. Nos. 5,054,713 and 2,726,829 have the bodies of their inventions intimately associated with a circular construction, and term their inventions as "circular" (wing) airplane. U.S. Pat. No. 5,031,859 refers to its invention as a thrust-producing device in its claims and elsewhere and teaches the method of "distributing . . . fluid . . . over and adjacent said surface for blanketing and enclosing . . . first stream" and "causing . . . first stream . . . unattached . . . to define a closed volume . . . " and then ". . . permitting . . . the first stream . . . to partially evacuate by entrainment the volume and to create a low pressure within the volume . . . " (see its abstract, paragraph two of column 2 of the specification, and claim 1)--this is a kind of pressure force method by entraining a volume of low pressure gas, which is not convincing as whether it will produce commercially significant lift force and whether it will work as described aerodynamically since no estimate of force magnitude is taught. Moreover, except for U.S. Pat. No. 3,697,020, the other five patents do not teach the use of supersonic flow and its aerodynamic expansion characteristic which are employed extensively in the present invention. Although U.S. Pat. No. 3,697,020 uses supersonic flow in a pressure force method, it does not use its expansion gas directly for forming the low pressure zone, instead it teaches the method with "The supersonically flowing gas separating and thereafter reattaching to the surface to provide a low pressure region intermediate the points of separation and reattachment" and "ambient gas trapped between the points of separation and reattachment [being] mixed with and entrained in the supersonic stream thereby creating a near vacuum . . . "--an entrainment method similar to that of patent U.S. Pat. No. 5,031,859. An additional important difference of the present invention is the use of an expansion space for the flow, which is produced by an increasing area of the flow front of a radial flow due to the front's increasing perimeter.